Introductionto.PDF

Introduction to Distributed Systems (DS) INF5040/9040 autumn 2012 lecturer: Frank Eliassen Frank Eliassen, Ifi/UiO 1 Outline  What is a distributed system?  Challenges and benefits of distributed system  Distribution transparencies  Pitfalls when developing distributed systems  Types of distributed systems Frank Eliassen, Ifi/UiO 2 1 What is a distributed system? Many definitions   [Coulouris]   A distributed system is one in which hardware or software components located at networked computers communicate and coordinate their actions only by passing messages.   [Tanenbaum van Steen]   A distributed system is a collection of independent computers that appears to its users as a single coherent system.   [Lamport]   A distributed system is a system that prevents you from doing any work when a computer you have never heard about, fails.   The above definitions take different perspectives   Operational perspective   User perspective   DS characteristcs perspective Frank Eliassen, Ifi/UiO 3 Implications of distributed systems   Concurrency –  components execute in concurrent processes that read and update shared resources. Requires coordination   No global clock –  makes coordination difficult (ordering of events)   Independent failure of components –  partial failure incomplete information   Unreliable communication –  Loss of connection and messages. Message bit errors   Unsecure communication –  Possibility of unauthorised recording and modification of messages   Expensive communication –  Communicatio